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U Scheer

Publications and source records attributed to U Scheer.

At least 73 records · Page 4Linked to original sources
PubMed1979

Injected histone antibodies interfere with transcription of lampbrush chromosome loops in oocytes of Pleurodeles.

Antibodies to calf thymus histone H2B were purified by chromatography on DEAE-cellulose and injected into oocyte nuclei of Pleurodeles waltlii. As shown by indirect immunofluorescence these antibodies cross-reacted strongly with corresponding histones associated with lampbrush chromosomes. Shortly after injection the lateral loops of the chromosomes retracted into the chromomeres and by 3 h postinjection the 'lampbrush' appearance was completely lost and the chromosomes appeared in light-microscopic preparations as rod-like structures consisting of longitudinally coalesced chromomeres. In control oocytes injected with non-immune immunoglobulins or antibodies against a ubiquitous transcript-associated protein no morphological alterations of the lampbrush chromosomes could be observed. Electron microscopic spreads of chromosomes prepared at various times after injection of anti-H2B revealed a progressive loss of transcriptional complexes from the loop axes. Finally, higher-order chromatin configurations, like supranucleosomal globules ('superbeads') or cable-like chromatin strands 50-60 nm thick predominated, indicating complete transcriptional inactivation of all chromosomal regions. The results indicate that H2B antibodies react specifically with histones associated with the transcribed DNA of lateral loops in their native state. The resulting antigen-antibody complexes seem to inhibit progression of the RNA polymerases along the template, thus causing the premature release of transcripts, a process analogous to the stripping effect of actinomycin D. The demonstration of histones associated with heavily transcribed regions, which are not compacted into nucleosomes but largely extended, supports the current concept that unfolding of nucleosomes to allow transcription of the DNA does not involve dissociation of histones. In contrast, amplified ribosomal RNA genes are unaffected by injected H2B antibodies. This does not necessarily indicate absence of histones from nucleolar chromatin, since we do not know whether it is accessible in vivo to antibodies or whether the histone antigenic determinants are masked by the presence of other proteins. The technique of injecting specific antibodies should be widely applicable when analysing the in vivo distribution of chromosomal components at the electron-microscopic level and when studying complex metabolic processes, like the cleavage and modification of RNA, by selective inhibition of defined enzymic steps.

Animals↗
PubMed1979

[The prognostic value of measuring cell size in acute childhood leukemia (author's transl)].

Prior to treatment we studied leukemia cell diameters in bone marrows of 89 children with acute lymphoblastic leukemia (ALL) and 26 children with myeloblastic leukemia (AML). Patients were treated according to the West-Berlin protocol. The median cell diameter (+/- S) in ALL measures 11,3 (+/- 1,1)mu, in AML 15,3 (+/- 1,1)mu. Both forms of leukemia show some overlapping of cell diameters in the range of 13,8--14,3 mu. with ALL, no difference is shown in the cell diameters of those who remained in complete remission or went into relapse. Likewise, there is no significant difference in cell-diameter, when correlating them to the following parameters: initial peripheral leucocyte count, acid phosphatase- and PAS-reaction, T-cellmarkers. The risk of relapse is the same in patients with more than 20% macrolymphoblasts (diameter greater than 12mu) and in those less than 20% macrolymphoblasts. In 11 patients with ALL cellmeasuring was performed during the first hematological relapse. The median cell-diameter in 10 of these cases is higher than in the initial bone marrow.

Acute Disease↗
PubMed1979

[Prognosis improvements in children with acute myelocytic leucemia after more intensive induction therapy (author's transl)].

Between October 1974 and October 1978 23 children with acute myelocytic leucemia (AML) received intensive therapy in the Univ.-Kinderklinik Münster: 4 children were treated according to the ALGB-protocol consisting of 5-7 day courses of ARA-C-infusion and 3 DNR-injections. 19 patients received the West-Berlin-protocol: The first 7 the original ALL protocol, 11 the modified form of AML, which will be presented here as AML-therapy-study BFM 78. 4 of the 23 patients died with early acute cerebral bleeding. 2 patients were nonresponders. 17 children went into remission. One girl died in remission of septicemic aspergillosis. 4 children had a relapse. In November 1978 there were still 12 patients in continuous complete remission, 3 of them already without therapy. 13 of the 19 patients, who were treated with the West-Berlin-protocol went into remission. 1 had a relapse. At present there are 11 patients in continuous complete remission. The above results and those found in the literature could signify that the long term prognosis of children with AML will be improved. To coordinate efforts toward this goal a cooperative AML-therapy-study in the "Deutsche Arbeitsgemeinschaft für Leukämieforschung" (BFM-group) using the here presented therapy protocol was formed in November 1978.

Adolescent↗
PubMed1978

Changes of nucleosome frequency in nucleolar and non-nucleolar chromatin as a function of transcription: an electron microscopic study.

The morphology of nucleolar and non-nucleolar (lampbrush chromosome loops) chromatin was studied in the electron microscope during states of reduced transcriptional activity in amphibian oocytes (Xenopus laevis, Triturus alpestris, T. cristatus). Reduced transcriptional activity was observed in maturing stages of oocyte development and after treatment with an inhibitor, actinomycin D. Strands of nucleolar chromatin appear smooth and thin, and contain only few, if any, nucleosomal particles in the transcribed units. This is true whether they are densely or only sparsely covered with lateral ribonucleoprotein fibrils. This smooth and non-nucleosomal character is also predominant in the interspersed, apparently nontranscribed rDNA spacer regions. During inactivation, however, nucleolar chromatin frequently and progressively assumes a beaded appearance in extended fibril-free--that is, apparently nontranscribed--regions. In either full-grown oocytes or late after drug treatment, most of the nucleolar chromatin is no longer smooth and thin, but rather shows a beaded configuration indistinguishable from inactive non-nucleolar chromatin. In many chromatin strands, transitions of fibril-associated regions of smooth character into beaded regions without lateral fibrils are seen. Similarly, in the non-nucleolar chromatin of the retracting lampbrush chromosome loops, reduced transcriptional activity is correlated with a change from smooth to beaded morphology. Here, however, beaded regions are also commonly found interspersed between the more or less distant bases of the lateral fibrils, the putative transcriptional complexes. In both sorts of chromatin, detergents (in particular Sarkosyl) that remove most of the chromatin proteins including histones from the DNA axis but leave the RNA polymerases of the transcriptional complexes attached were used to discriminate between polymerases and nucleosomal particles. The results suggest that nucleosomes are absent in heavily transcribed chromatin regions but are reformed after inactivation. In contrast to the findings with inactivated nucleolar genes, in lampbrush chromosome loops the beaded nucleosomal configuration appears to be assumed also in regions within transcriptional units that, perhaps temporarily, are not involved in transcription.

Animals↗
PubMed1977

Lengths and patterns of transcriptional units in the amplified nucleoli of oocytes of Xenopus laevis.

Transcriptionally active chromatin from peripheral amplified nucleoli of lampbrush-chromosome stage oocytes of Xenopus laevis was dispersed and spread in various solutions of low salt concentrations (including some with additions of detergents) and examined by electron microscopy. Nucleolar material from oocytes of animals with normal (2-nu) and mutant (1-nu) genetical constitution of nucleolus organizers was compared. Histograms showing the distributions of the length of matrix units, apparent spacer intercepts, and the total repeating units of the rDNA containing chromatin axes revealed a significant degree of heterogeity, with indications of subclasses and predominant repeat unit size classes of 3.3 amd 3.8 micron length. The correspondence of matrix unit length to the molecular weight of the first stable product of rDNA transcription was studied using gel electrophoresis of labelled pre-rRNA under non-denaturing and denaturing conditions. Evaluations of individual strands of nucleolar chromatin further demonstrated the existence of both (i) strands with obviously homogeneous repeating units of and (ii) strands with intra-axial heterogeneity of rDNA subunits. "Prelude complexes", i.e. groups of transcriptional complexes in apparent spacer intercepts, were not infrequently noted. The data are compared with the measurements of lengths of repeating units in fragments of rDNA obtained by digestion with EcoRI endonuclease as described by Morrow et al.(1974) and Wellauer et al. (1974,1976a, b). The results are discussed in relation to problems of variations in the modes of arrangement of the pre-rRNA genes, the state of packing of rDNA during transcription, and possible mechanisms of the amplification process.

Animals↗
PubMed1977

Frequencies of circular units of nucleolar DNA in oocytes of two insects, Acheta domesticus and dytiscus marginalis, and changes of nucleolar morphology during oogenesis.

The organization of the extrachromosomal nucleolar material in oocytes of two insect species with different ovary types, the house cricket Acheta domesticus (panoistic ovary) and the water beetle Dytiscus marginalis (meroistic ovary), was studied with light and electron microscopic techniques. Stages early in oogenesis were compared with fully vitellogenic stages (mid-to-late diplotene). The arangement of the nucleolar material undergoes a marked change from a densely aggregated to a dispersed state. The latter was characterized by high transcriptional activity. In spread and positively stained preparations of isolated nucleolar material, a high frequency of small circular units of transcribed rDNA was observed and rings with small numbers (1--5) of pre-rRNA genes were predominant. The observations suggest that the 'extra DNA body' observed in early oogenic stages of both species represents a dense aggregate ofnumerous short circular units of nucleolar chromatin, with morphological subcomponents identifiable in ultrathin sections. These apparently remain in close association with the chromosomal nucleolar organizer(s). The observations further indicate that the individual small nucleolar subunit circles dissociate and are dispersed as actively transcribed rDNA units later in diplotene. The results are discussed in relation to principles of the ultrastructural organization of nucleoli in other cell types as well as in relation to possible mechanisms of gene amplification.

Animals↗
PubMed1976

Experimental disintegration of the nuclear envelope. Evidence for pore-connecting fibrils.

The disintegration of the nuclear envelope has been examined in nuclei and nuclear envelopes isolated from amphibian oocytes from amphibian oocytes and rat liver tissue, using different electron microscope techniques (ultrathin sections and negatively or positively stained spread preparations). Various treatments were studied, including disruption by surface tension forces, very low salt concentrations, and nonionic detergents such as Triton C-100 and Nonidet P-40. The highest local stability of the cylinders of nonmembranous pore complex material is emphasized. As progressive disintegration occurred in the membrane regions, a network of fibrils became apparent which interconnects the pore complexes and is distinguished from the pore complex-associated about 15-20 nm thick, located at the level of the inner nuclear membrane, which is recognized in thin sections to bridge the interpore distances. With all disintegraiton treatments a somewhat higher susceptibility of the outer nuclear membrane is notable, but a selective removal does not take place. Final stages of disintegration are generally characterized by the absence of identifiable, membrane-like structures. Analysis of detergent-treated nuclei and nuclear membrane fractions shows almost complete absence of lipid components but retention bo significant amount of glycoproteins with a typical endomembrane-type carbohydrate pattern. Various alternative interpretations of these observations are discussed. From the present observations and those of Aaronson and Blobel (1,2), we favor the notion that threadlike intrinsic membrane components are stabilized by their attachment to the pore complexes, and perhaps also to peripheral nuclear structures,and constitute a detergent-resistant, interpore skeleton meshwork.

Animals↗
PubMed1976

Regulation of transcription of genes of ribosomal rna during amphibian oogenesis. A biochemical and morphological study.

Natural changes in the transcription of rRNA genes were studied in nucleoli from three oogenic stages of the newt Triturus alpestris with electron microscope, auto-radiographic, and biochemical techniques. From determinations of the uridine triphosphate pool sizes and [3H]uridine uptake, phosphorylation, and incorporation into 28S and 18S rRNAs in vivo it was estimated that the rate of rRNA synthesis was about 0.01% in previtellogenic oocytes and 13% in mature oocytes when compared to midvitellogenesis. Spread preparations of nucleoli showed significant morphological changes in the transcriptional complexes. The total number of lateral fibrils, i.e., ribonucleoproteins containing the nascent rRNA precursor, were drastically decreased in stages of reduced synthetic activity. This indicates that rRNA synthesis is regulated primarily at the level of transcription. The resulting patterns of fibril coverage of the nucleolar chromatin axes revealed a marked heterogeneity. On the same nucleolar axis occurred matrix units that were completely devoid of lateral fibrils, matrix units that were almost fully covered with lateral fibrils, and various forms of matrix units with a range of lateral fibril densities intermediate between the two extremes. Granular particles that were tentatively identified as RNA polymerase molecules were not restricted to the transciptional complexes. They were observed, although less regularly and separated by greater distances, in untranscribed spacer regions as well as in untranscribed gene intercepts. The results show that the pattern of transcriptional control of rRNA genes differs widely in different genes, even in the same genetic unit.

Animals↗
PubMed1976

Classification of loops of lampbrush chromosomes according to the arrangement of transcriptional complexes.

The arrangement of transcriptional units in the loops of lampbrush chromosomes from oocyte nuclei of urodele amphibia and from primary nuclei of the green alga Acetabularia have been studied in the electron microscope using spread preparations. Loops with different patterns of arrangement of matrix units (i.e. to a first approximation, transcriptional units) can be distinguished: (i) loops consisting of one active transcriptional unit; (ii) loops containing one active transcriptional unit plus additional fibril-free, i.e. apparently untranscribed, intercepts that may include 'spacer' regions; (iii) loops containing two or more transcriptional units arranged in identical or changing polarities, with or without interspersed apparent spacer regions. Morphological details of the transcriptional complexes are described. The observations are not compatible with the concept that one loop reflects one and only one transcriptional unit but, rather, lead to a classification of loop types according to the arrangement of their transcriptional units. We propose that the lampbrush chromosome loop can represent a unit for the coordinate transcription of either one gene or a set of several (different) genes.

Acetabularia↗
PubMed1975

Lampbrush-type chromosomes in the primary nucleus of the green alga Acetabularia mediterranea.

Structures with a lampbruch-chromosome-like morphology are described in the nucleoplasm of primary nuclei of the green alga, Acetabularia mediterranea, by light and electron microscopy in sections of cells fixed in situ and in spread preparations of isolated nuclear components. These chromosomes reveal typical loops (up to 20 micronm long), chromomere-like nodules (1-2 micronm in diameter), and 2-4 micronm large axial globules. Associations of some of these chromosomes with nucleolar structures and with the nuclear envelope are also recognized. The light microscopically identified loops are correlated with distinct fibrillogranular structures observed in the thin sections and with the very long matrix units seen in the spread preparations. The similarity of these structures to the lampbrush chromosomes of various animal cell types, all exclusively stages of meiotic prophase, is discussed as well as the possible relation of the appearance of lampbrush chromosomes to a defined phase of the vegatative growth of this alga.

Acetabularia↗